Bastards are not allowed to inherit their father's lands or titles, and have no claims to the privileges of their father's House. It is up to their father on how to raise or treat them: at worst they are unacknowledged and ignored, though they may fare better and be discreetly sent funds to ensure their well-being. At best, a lord will acknowledge his bastard children (allowing them to take on one of the special bastard surnames), but send them away to one of his distant castles to be raised away from his lawful family. For bastard children to be raised by their father in his own castle alongside his trueborn children is considered extremely unusual (such as when Eddard Stark did so for his bastard son, Jon Snow).

Faced with no prospects for inheritance, many noble-born bastards, even acknowledged ones, ultimately voluntarily join the Night's Watch to seek prestige and equality. The Night's Watch is highly egalitarian compared to the rest of Westeros, and at the Wall every man is given what he earns; both bastards and criminals can become high-ranking officers and commanders for their service. Similarly, bastards may also take up the life of knighthood in the hope of being granted a place at a lord's household and even lands and titles for services to their liege lords. In this way, a bastard may become the founder of a noble house. Bastard children may also be given over to the Faith of the Seven to join monastic orders or the clergy, and bastard sons may be sent to train as Maesters.

There is no outright law punishing noble men or women for having bastard children, instead it is considered a social and religious disgrace.

It is possible for the king to legitimize a lord's bastard children, though this special dispensation is difficult to acquire and infrequently happens.[1] It will usually only be granted if a lord has no other legitimate children (or no male children) to carry on the name of his house. However, the social stigma is not automatically removed after the bastard is formally legitimized.

Nevertheless, as a highborn bastard carries the blood of a noble house, they may still be perceived as a potential threat by rival claimants. For this reason, King Joffrey orders the massacre of all of his father's illegitimate offspring (though, ironically, Joffrey and his siblings are all secretly bastards born of incest between Cersei and Jaime Lannister, and Joffrey appears to be aware of this, for which he orders the massacre of Robert's true children and stronger claimants).[2] When Roose Bolton and Ramsay Snow discuss their search for the remaining male Stark children, Ramsay suggests killing Ned Stark's bastard son Jon Snow too. He reasons that, being of Stark blood, Jon could become a threat to their rule in the North.[3]

Due to its unique history and culture, bastards are not looked down upon in Dorne the way they are in the rest of the Seven Kingdoms. The present-day Dornishmen descend from the Rhoynar people who migrated to Westeros a thousand years ago, whose possessed an urban culture based around city-states along the Rhoyne River in Essos. The culture they passed down to the present-day Dornishmen has relatively relaxed attitudes towards sexual matters. While the Rhoynar who came to Dorne did convert to the Faith of the Seven, they basically just ignored the rules they didn't like, and follow the religion much less strictly than other parts of Westeros. Many Dornish nobles have formalized lovers known as paramours, and they do not possess the same stigma against homosexual behavior that the rest of Westeros does.

These relaxed sexual mores in Dorne extend to bastard children. The Dornish feel that bastards are born of passion and love, unlike the rest of the Seven Kingdoms that consider them born of lies and deceit, and thus would not disdain a child for such a parentage. While it is rare and scandalous for a lord from outside of Dorne to raise his bastard child in his home castle alongside his trueborn children (i.e. as Eddard Stark did with Jon Snow), it is actually commonplace in Dorne to see bastards living at the court of their noble parents; Oberyn Martell raised his eight illegitimate daughters in Sunspear, alongside his brother's legitimate children. The Dornish are also much more likely to acknowledge any bastard children in the first place: they would consider it cruel for a lord to abandon his own flesh and blood, as King Robert Baratheon ignored the many bastard children he fathered over the years. Because Dornish culture holds little if any stigma against bastards, it is not unusual to see bastards work their way up to important social or court positions there, holding castles or leading armies for their families.

Bastards in Dorne still face a few restrictions, but they are relatively minor compared to the social contempt that bastards in the rest of the Seven Kingdoms often face. Bastards in Dorne must still use the special bastard surname "Sand", and they are less likely to inherit from their parents. While Jon Snow was roughly the same age as his father's eldest trueborn son, Robb Stark, he was still shooed outside during the great feast at Winterfell, rather than potentially offend King Robert and Queen Cersei by seating a bastard at the main table. The Dornish, in contrast, feel that an older bastard does have a place within the family and is not shameful, but a bastard child is treated somewhat like a younger child in order of inheritance. For example, if the Starks lived in Dorne, Jon Snow would be treated as a younger brother behind even Rickon in the line of succession, but otherwise, he would be treated as a full member of the family.

Another minor stigma against bastards in Dorne is that it is still seen as marrying beneath one's station for a powerful lord to marry a noble-born bastard. This is often simply due to the practical reason that a bastard cannot inherit, and thus the marriage would not bring with it any new wealth or lands. This stigma is somewhat like if a nobleman married a daughter from another House who was trueborn, but who was also the fifth youngest of five daughters, and thus a very poor match. Ellaria Sand is an acknowledged bastard of House Uller, one of the more powerful noble families in Dorne. Even in the relaxed social mores of Dorne, however, it would still have been marrying beneath his station for Prince Oberyn Martell, younger brother of the ruler of Dorne, to wed Ellaria. While Oberyn could not marry Ellaria, he simply made her his formal paramour, his wife in all but name.

The stigma of illegitimacy is so great, that all acknowledged bastards born to a noble in Westeros have to identify themselves through a specific surname marking them as a bastard, which varies by region:

However, this system does not apply to the bastards of smallfolk: at least one parent (usually, but not always, the father) has to be a member of a noble House. If both the father and mother are commoners, the child cannot use the special surname.

The low-born commoners of Westeros do not actually use surnames at all. Therefore, possessing a bastard surname is simultaneously a mark of distinction and badge of shame. Anyone who encounters someone with a bastard surname will immediately know that they are not simply a bastard, but the bastard child of a noble.

Gendry, as an unacknowledged bastard of Robert Baratheon, cannot use the surname "Waters".

Bastards only use the special surnames if they have been openly acknowledged by their noble-born parent. In such cases, their noble parent will usually try to make sure that they are well cared for, or send money for their support, but it is extremely unusual for a noble to raise their bastard child in their own household.
There is no official distinction between bastards who have one noble-born parent, and those whose parents are both noble-born. In practice, however, a nobleman would be much more likely to acknowledge a bastard child born to a noble lady, than he would a child born to a commoner.

Bastard surnames are dependent on the region a child was born in, i.e. where the mother is from, not where the father is from. For example, a noble lord from the Stormlands could father one bastard child in the Vale, and another in the Riverlands, but neither would use the surname "Storm": the first bastard would use the surname "Stone", and the second would use the surname "Rivers." It is extremely unusual for a bastard to know who his nobleman father is, but not his mother. Therefore Jon Snow's situation is additionally unusual, not just because he actually lives with his nobleman father, but because he probably wasn't even born in the North. Eddard Stark brought him back to Winterfell as an infant after fighting in the south during Robert's Rebellion, but refused to say who his mother was or where she came from. As a result of the mystery surrounding his mother's identity, Jon ended up using the surname "Snow" by default.

Bastard children of a noble lord may be referred to politely as "natural children", though the less polite term "baseborn" is more commonly used, and they are often bluntly and rudely referred to as simply "bastard." In contrast, a noble lord's children with his lawfully married wife are termed "trueborn". Thus when Lord Eddard Stark discovers that none of Cersei Lannister's children were fathered by her husband King Robert Baratheon, he says that King Robert "has no trueborn sons," even though he knows that Robert has several "baseborn," bastard children.[4]

In the A Song of Ice and Fire novels, the status of being a bastard is a considerable social disgrace amongst the nobility, though less so amongst the smallfolk. However, while bastards are disadvantaged, they still have means to climb the social ladder. They may win honor and glory in battle and be knighted. If they do great deeds in service to the king or a noble lord, they can even receive a bill of legitimacy, allowing them to take their father's surname and formally join his House, or to take a new surname and found a new House (some bastards take new names altogether, like "Blackfyre", while others add a prefix to their bastard name, such as "Longwaters"). For example, House Baratheon was founded by the legitimized bastard half-brother of Aegon the Conqueror.

However, while bastards stand outside the lines of succession and inheritance, there are still exceptions which have caused immense problems. King Aegon IV Targaryen legitmized three of his bastard sons and one of his bastard daughters on his deathbed. His eldest bastard son, Daemon Blackfyre, later claimed the Iron Throne and led a bloody civil war known as the First Blackfyre Rebellion . His sons and descendants launched four more attempts to take the Iron Throne before their final claimant, Maelys the Monstrous, was slain by Ser Barristan Selmy during the War of the Ninepenny Kings. This is sometimes used as an example of what happens if a bastard is treated too well and given too much power and legitimacy.

There is no official distinction between bastards who have one noble-born parent, and those whose parents are both noble-born. In practice, however, a nobleman would be much more likely to acknowledge a bastard child born to a noble lady, than he would a child born to a commoner. For example, while Robert Baratheon is rumored to have fathered over a dozen bastard children, the only one who he acknowledged in the books was Edric Storm, because his mother was a noblewoman, Delena of House Florent - the younger first cousin of Selyse Florent, the wife of Robert's younger brother Stannis.

Fans sometimes derisively assume that "Joffrey Baratheon" should really be called "Joffrey Lannister", because of his status as the bastard offspring of the incestuous relationship between Cersei Lannister and Jaime Lannister, and not the son of King Robert Baratheon at all. This is actually in error, as according to the customs of bastardy, Joffrey doesn't even have the right to use the surname "Lannister". As Jaime's bastard son, given birth to by a woman from the Westerlands (Cersei), Joffrey would have to use the bastard surname for the Westerlands: "Joffrey Hill". There's also the possibility that he might be called "Joffrey Waters" given that both Jaime and Cersei had been living in the Crownlands for many years, and Joffrey lived his whole life there. All of this, of course, would only happen if Jaime were to openly acknowledge Joffrey as his son, which is an impossibility given the disastrous political fallout this would create. Further, as the product of not merely bastardy, but incest, the Faith of the Seven would want to outright kill Joffrey as an abomination before the gods if his actual parentage were ever revealed. Therefore from a strict legal standpoint, given that Jaime will never acknowledge his children with Cersei, Joffrey has no right to any surname, and should properly just be called "Joffrey" as if he were a lowborn commoner.